1. Field of the Invention
The present invention relates to the field of amplifiers. In particular, the present invention is related to the of field quiescent current control in class AB (push-pull) amplifiers used in analog circuits.
2. Related Art
Class AB type amplifiers are widely used in analog circuits for their higher power efficiency, as compared, for example, to class A amplifiers. In class AB amplifiers, control of quiescent current in the amplifier's output stage is critical since it affects standby power and crossover distortion. Among various class AB amplifier architectures, the floating class conventional AB control amplifiers are commonly used for their simple quiescent current control scheme.
Quiescent current control schemes are generally designed to minimize the level and variation of this current within amplifiers in general, and class AB amplifiers in particular. If the quiescent current (Iq) is a high value, the Iq is easier to control and the amplifier's non-linearity performance is better. However, a high quiescent current (Iq) translates to greater power consumption in standby mode. On the other hand, a low quiescent current (Iq) value means the amplifier's non-linearity is high and the cross over distortion will also be high. If the quiescent current (Iq) is very small, the amplifier's accuracy will also be low, with high variations over its operational ranges.
A major shortcoming of these convention amplifier quiescent current control schemes is that Iq varies significantly with process, supply voltage and temperature variations. These variations are one of the features that make these traditional class AB amplifiers undesirable for low power applications.
What is needed, therefore, is a more robust technique to minimize variations in the quiescent current (Iq) flowing through the output stage of push pull amplifiers, such as the class AB amplifier.